Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$86.86	4.258%	$90.5585	$90.56	$90.55	$90.60
Purchase #2	$200.88	7.325%	$215.5945	$215.59	$215.60	$215.60
Purchase #3	$40.89	3.284%	$42.2328	$42.23	$42.25	$42.20
Purchase #4	$167.73	7.127%	$179.6841	$179.68	$179.70	$179.70
Purchase #5	$13.48	7.330%	$14.4681	$14.47	$14.45	$14.50
Purchase #6	$194.90	8.400%	$211.2716	$211.27	$211.25	$211.30
Purchase #7	$21.77	11.795%	$24.3378	$24.34	$24.35	$24.30
7 purchase totals =	$726.51		$778.1474	$778.14	$778.15	$778.20